Abstract of
CA2294004
A first linear sensor array (42) produces, at a first time of occurence, a first image of a segment of an object (12) as the object moves across the sensor at a variable speed. The image and its time of occurrence are accumulated in a buffer. As the object continues to move across the sensor, a successive plurality of the segment images seen by the first sensor are accumulated in the buffer, together with their respective times of occurrence. A second linear sensor array (44) spaced a distance from the first array produces, at a second time of occurrence, a second image of another segment of the moving object. The second image is compared with the accumulated first images to determine which of the accumulated first images is most similar to the second image. The object's speed S can then be estimated as an appropriately weighted function of d/(tj-tm) í.e. S d/(tj-tm)!, where tj is the time of occurrence of a selected one of the second images and tm is the time of occurrence of the first image most similar to the selected second image. By continually monitoring the object's speed in this fashion, one may select and transfer into an image buffer those image segments which together form the highest quality image of the object, independently of the object's speed of motion past the sensor and without the need for expensive, bulky stepper motors, mechanical motion encoders, or the like.
(a) a first linear sensor array (42) for producing,
at a first time of occurrence, a first image of
a first segment of an object positioned adjacent
said first sensor;
(b) a buffer (24) coupled to said first array, said
buffer for accumulating said first image and said
first time of occurrence for a successive plural
ity of said first segments as said object moves
across said first array;
(c) a second linear sensor array (44) spaced from
said first array by a distance d, said second
array for producing, at a second time of occur
rence, a second image of a second object segment
positioned adjacent said second sensor;
(d) a comparator (22) coupled between said buffer and
said second array, said comparator for comparing
said second image with each one of said accumu
lated first images and for determining which one
of said accumulated first images is most similar
to said second image; and,
(e) an object speed estimator (22) for estimating
said object's speed S ocd/(ti-tm), wheretj is said
time of occurrence of a selected one of said
second images andtrn is said time of occurrence
of said first image most similar to said selected
second image.
2. Imaging apparatus as defined in claim 1, further
characterized by sensor control means (22) coupled
between said object speed estimator and said first
array, said sensor control means for controlling
timing between successive ones of said first time of
occurrence as a function of said speed S.
3. An imaging method characterized by the steps of:
(a) producing, at a first time of occurrence, a first
image of a first segment of an object positioned
in a first location;
(b) accumulating said first image and said first time
of occurrence;
(c) repeating said steps (a) and (b) for a successive
plurality of said first segments as said object
moves across said first location;
(d) producing, at a second time of occurrence, a
second image of a second segment of said object
positioned in a second location spaced a distance
d from said first location;
(e) comparing said second image with said accumulated
first images and selecting that one of said
accumulated first images which is most similar to
said second image;
(f) estimating said object's speed Soc d/(ti-tm),
where ti is said time of occurrence of a selected
one of said second images and tm is said time of
occurrence of said first image most similar to
said selected second image;
(g) storing said speed estimate with said selected
first image;
(h) repeating said steps (a) through (g) until said
object moves beyond said second location; and,
(i) combining said selected first images to produce
a composite image of said object.
4. An imaging method as defined in claim 3, wherein:
(a) said segment images are each produced during a
time interval of fixed duration T; and,
(b) said combining step further comprises, for each
one of said selected first segment images, resiz
ing said selected first segment image from a
width w =Si * T to a constant width, whereSj is
said speed estimate stored with said selected
first segment image.
5. Imaging apparatus, characterized by:
(a) a linear sensor array (10) for sequentially
producing images of segments of an object (12) as
said object moves transversely across said array
to successively position said segments adjacent
said sensor;
(b) a comparator (22) for comparing a selected pair
of said segment images and for producing an
output signal (26) representative of similarity
therebetween; and,
(c) a buffer (24) for accumulating said segment
images whenever said comparator output signal is
not representative of substantial similarity
between said pair of images.
6. An imaging method characterized by the steps of:
(a) sequentially detecting segments of an object
while said segments are successively positioned
within a predefined linear region and while said
object moves transversely across said region;
(b) producing images of each of said detected object
segments;
(c) comparing said images with stored representations
of previously detected images of said respective
segments; and,
(d) accumulating said image of said detected object
segment whenever said compared images are not
substantially similar.
7. An imaging method characterized by the steps of:
(a) after expiry of a time intervalTwat, producing at
a first time of occurrence, a first image of a
first segment of an object positioned in a first
location;
(b) accumulating said first image and said first time
of occurrence;
(c) repeating said steps (a) and (b) for a successive
plurality of said first segments as said object
moves across said first location;
(d) producing, at a second time or occurrence, a
second image of a second segment of said object
positioned in a second location spaced a distance
d from said first location;
(e) comparing said second image with each one of said
accumulated first images and selecting that one
of said accumulated first images which is most
similar to said second image;
(f) estimating said object's speed Soc d/(ti-tm),
where ti is said time of occurrence of a selected
one of said second images and tm is said time of
occurrence of said first image most similar to
said selected second image;
(g) determining said time intervalTwait =1/(R * S)
where R is a predefined image resolution;
(h) repeating said steps (a) through (g) until said
object moves beyond said second location; and,
(i) combining said selected first images to produce
a composite image of said object.
8. Imaging apparatus, characterized by:
(a) a first linear sensor array (84) for producing,
at a first time of occurrence, a first image of
a first segment of an object positioned adjacent
said first sensor;
(b) a buffer (24) coupled to said first array, said
buffer for accumulating said first image and said
first time of occurrence for a successive plural
ity of said first segments as said object moves
across said first array;
(c) a second linear sensor array (86) spaced from
said first array by a distance d12, said second
array for producing, at a second time of occur
rence, a second image of a second object segment
positioned adjacent said second sensor; (d) a third linear sensor array (88) spaced from said
first array by a distance d13 and spaced from said
second array by a distance d23, said third array
for producing, at a third time of occurrence, a
third image of a third object segment positioned
adjacent said third sensor; (e) a comparator (22) coupled between said buffer and
said second and third arrays, said comparator
for:
(i) comparing said second image with each one of
said accumulated first images and for deter
mining which one of said accumulated first
images is most similar to said second image;
(ii) comparing said third image with each one of
said accumulated first images and for deter
mining which one of said accumulated first
images is most similar to said third image;
and, (f) an object speed estimator (22) for estimating
said object's speed S as proportional to any one
of:
(i)d12/(tj -; or,
(ii) d23/ (tm - to) ;or, (iii) d13/ (tj - to) or,
(iv) a combination ofd12/(tj -try), d23/(tk -to)
and d13/ (tj -to);
where tj is said time of occurrence of a selected
one of said second images, tk is said time of
occurrence of said first image most similar to
said selected second image, and to is said time of
occurrence of said third image most similar to
said selected second image.
9. Imaging apparatus as defined in claim 8, further
characterized by sensor control means coupled between
said object speed estimator and said second array,
said sensor control means for controlling timing
between successive ones of said first time of occur
rence as a function of said speed S.
10. An imaging method characterized by the steps of:
(a) producing, at a first time of occurrence, a first
image of a first segment of an object positioned
in a first location;
(b) accumulating said first image and said first time
of occurrence;
(c) repeating said steps (a) and (b) for a successive
plurality of said first segments as said object
moves across said first location;
(d) producing, at a second time of occurrence, a
second image of a second segment of said object
positioned in a second location spaced a distance
d12 from said first location;
(e) producing, at a third time of occurrence, a third
image of a third segment of said object posi
tioned in a third location spaced a distance d13
from said first location and spaced a distance d23
from said second location;
(f) comparing said second image with each one of said
accumulated first images and selecting that one
of said accumulated first images which is most
similar to said second image;
(g) comparing said third image with each one of said
accumulated first images and selecting that one
of said accumulated first images which is most
similar to said third image;
(h) estimating said object's speed S as proportional
to any one of:
(i)d12/(tj-tm); or,
(ii)dl3/(tk-to) ; or,
(iii) d23/(tm-to); or, <RTI (iv) a combination of d12/(tj - tm) , d23/(tm - to)
andd13/ (tk -to);
where tj is said time of occurrence of a selected
one of said second images, tk is said time of
occurrence of said first image most similar to
said selected second image, and to is said time of
occurrence of said first image most similar to
said selected third image;
(i) repeating said steps (a) through (h) until said
object moves beyond said third location; and,
(j) combining said selected first images to produce
a composite image of said object.
11. An imaging method as defined in claim 10, wherein:
(a) said segment images are each produced during a
time interval of fixed duration T; and,
(b) said combining step further comprises, for each
one of said selected first segment images, resiz
ing said selected first segment image from a
width w =Sj * T to a constant fixed width, where
Sj is said speed estimate determined with respect
to said selected first segment image.
12. An imaging method as defined in claim 10, further
characterized by, after said speed estimating step,
determiningTwait =1/(R * S) where R is a predefined
image resolution and then waiting for a time interval
equal toTwait after said step12 (a) before continuing
performance of said method.
13. Imaging apparatus, characterized by:
(a) a first linear sensor array for producing, at a
first time of occurrence, a first image of a
first segment of an object positioned adjacent
said first sensor; (b) a first coloured filter for colour filtering said
first image; (c) a first buffer coupled to said first array, said
first buffer for accumulating said colour fil
tered first image and said first time of occur
rence for a successive plurality of said first
segments as said object moves across said first
array; (d) a second linear sensor array spaced from said
first array by a distance d12, said second array
for producing, at a second time of occurrence, a
second image of a second object segment posi
tioned adjacent said second sensor; (e) a second coloured filter for colour filtering
said second image; (f) a second buffer coupled to said second array,
said second buffer for accumulating said colour
filtered second image and said second time for a
successive plurality of said second segments as
said object moves across said second array; (g) a third linear sensor array spaced from said
first array by a distance d13 and spaced from said
second array by a distance d23, said third array
for producing, at a third time of occurrence, a
third image of a third object segment positioned
adjacent said third sensor; (h) a third coloured filter for colour filtering said
third image; (i) a third buffer coupled to said third array, said
third buffer for accumulating said colour fil
tered third image and said third time for a
successive plurality of said third segments as
said object moves across said third array; (j) a first comparator coupled between said first
buffer and said second array, said first compara
tor for comparing said second colour filtered
image with each one of said accumulated first
colour filtered images and for determining which
one of said accumulated first colour filtered
images is most similar to said second colour fil
tered image;
(k) a second comparator coupled between said second
buffer and said third array, said second compar
ator for comparing said third colour filtered
image with each one of said accumulated second
colour filtered images and for determining which
one of said accumulated second colour filtered
images is most similar to said third colour fil
tered image;
(1) a third comparator coupled between said third
buffer and said first array, said third compara
tor for comparing said first colour filtered
image with each one of said accumulated third
colour filtered images and for determining which
one of said accumulated third colour filtered
images is most similar to said first colour fil
tered image;
(m) a first object speed estimator for estimating
said object's speed S ocd12/(tc-ta) where tc is
said time of occurrence of a selected one of said
first colour filtered images and ta is said time
of occurrence of said second colour filtered
image most similar to said selected first colour
filtered image;
(n) a second object speed estimator for estimating
said object's speed S ocdi3/(tc), where tb is
said time of occurrence of said third colour
filtered image most similar to said selected
first colour filtered image; and,
(o) a third object speed estimator for estimating
said object's speed S ocd23/(ta-tb).
14. An imaging method characterized by the steps of: (a) producing, at a selected time of occurrence, a
first colour filtered image of a first segment of
an object positioned in first location; (b) producing, at a selected time of occurrence, a
second colour filtered image of a second segment
of said object while said second segment is posi
tioned in a second location spaced from said
first location; (c) producing, at a selected time of occurrence, a
third colour filtered image of a third segment of
said object while said third segment is posi
tioned in a third location spaced from said first
and second locations; (d) accumulating said images and said respective
times of occurrence; (e) repeating said steps (a) through (d) for success
ive pluralities of said first, second, and third
segments as said object moves across said first,
second, and third locations respectively; (f) producing, at a selected time of occurrence, a
fourth non colour filtered image of a fourth
segment of said object while said fourth segment
is positioned in a fourth location spaced from
said first, second and third locations; (g) comparing said fourth image with each one of said
accumulated first images and selecting that one
of said accumulated first images which is most
similar to said fourth image; (h) comparing said fourth image with each one of said
accumulated second images and selecting that one
of said accumulated second images which is most
similar to said fourth image; (i) comparing said fourth image with each one of said
accumulated third images and selecting that one
of said accumulated third images which is most
similar to said fourth image;
(j) estimating said object's speed S ocQ4/(tctR),
d24/(tC~to) andd34/(tC-tB) where d14 is said spac
ing between said first and fourth sensors, d24 is
said spacing between said second and fourth sen
sors, d34 is said spacing between said third and
fourth sensors, tc is said time of occurrence of
a selected one of said non colour filtered
images, tR is said time of occurrence of said
first colour filtered image most similar to said
selected non colour filtered image, tG is said
time of occurrence of said second colour filtered
image most similar to said selected non colour
filtered image and tB is said time of occurrence
of said third colour filtered image most similar
to said selected non colour filtered image; and,
(k) repeating said steps (a) through (j) until said
object moves beyond said fourth location; and,
(1) combining said selected first images to produce
a composite image of said object.
15. An imaging method as defined in claim 14, wherein:
(a) said segment images are each produced during a
time interval of fixed duration T; and,
(b) said combining step further comprises:
(i) for each one of said selected first segment
images, resizing said selected first segment
image from a width w =SR * T to a constant
fixed width, whereSR is said speed estimate
determined with respect to said selected
first segment image;
(ii) for each one of said selected second images,
resizing said selected second image from a
width w =SG * T to a constant fixed width,
whereSG is said speed estimate determined
with respect to said selected second image;
and,
(iii) for each one of said selected third
images, resizing said selected third
image from a width w =SB * T to a
constant fixed width, whereSB is said
speed estimate determined with respect
to said selected third image.
16. An imaging method as defined in claim 14, further
characterized by, after said speed estimating step,
determiningTwait = 1/(R * S) where R is a predefined
image resolution and then waiting for a time interval
equal toTwait after said step15 (a) before continuing
performance of said method.
17. Imaging apparatus, characterized by:
(a) a first linear sensor array (106) for producing,
at a first time of occurrence, a first image of
a first segment of an object positioned adjacent
said first sensor;
(b) a first coloured filter for colour filtering said
first image;
(c) a first buffer coupled to said first array, said
first buffer for accumulating said colour fil
tered first image and said first time of occur
rence for a successive plurality of said first
segments as said object moves across said first
array;
(d) a second linear sensor array (108) spaced from
said first array said second array for producing,
at a second time of occurrence, a second image of
a second object segment positioned adjacent said
second sensor;
(e) a second coloured filter for colour filtering
said second image;
(f) a second buffer coupled to said second array,
said second buffer for accumulating said colour
filtered second image and said second time for a
successive plurality of said second segments as
said object moves across said second array; (g) a third linear sensor array (110) spaced from
said first and second arrays, said third array
for producing, at a third time of occurrence, a
third image of a third object segment positioned
adjacent said third sensor; (h) a third coloured filter for colour filtering said
third image; (i) a third buffer coupled to said third array, said
third buffer for accumulating said colour fil
tered third image and said third time for a
successive plurality of said third segments as
said object moves across said third array; (j) a fourth linear sensor array (112) spaced from
said first, second and third arrays, said fourth
array for producing, at a fourth time of occur
rence, a fourth non colour filtered image of a
fourth object segment positioned adjacent said
fourth sensor; (k) a first comparator coupled between said first
buffer and said fourth array, said first compara
tor for comparing said non colour filtered image
with each one of said accumulated first colour
filtered images and for determining which one of
said accumulated first colour filtered images is
most similar to said non colour filtered image; (1) a second comparator coupled between said second
buffer and said fourth array, said second compar
ator for comparing said non colour filtered image
with each one of said accumulated second colour
filtered images and for determining which one of
said accumulated second colour filtered images is
most similar to said non colour filtered image; (m) a third comparator coupled between said third
buffer and said fourth array, said third compara
tor for comparing said non colour filtered image
with each one of said accumulated third colour
filtered images and for determining which one of
said accumulated third colour filtered images is
most similar to said non colour filtered image; (n) a first object speed estimator for estimating
said object's speed S ocd14/(tc-tR), where d14 is
said spacing between said first and fourth sen
sors, tc is said time of occurrence of a selected
one of said non colour filtered images and tR is
said time of occurrence of said first colour
filtered image most similar to said selected non
colour filtered image; (o) a second object speed estimator for estimating
said object's speed S ocd24/(tC-tG), where d24 is
said spacing between said second and fourth sen
sors,tG is said time of occurrence of said
second colour filtered image most similar to said
selected non colour filtered image; and, (p) a third object speed estimator for estimating
said object's speed S ocd34/(tC-tB), where d34 is
said spacing between said third and fourth sen
sors,t13 is said time of occurrence of said third
colour filtered image most similar to said
selected non colour filtered image.
Description
LINEAR SENSOR IMAGING METHOD AND APPARATUS
Technical Field
This application pertains to a method and apparatus for inexpensively capturing an image of an object which moves, at an unknown variable or constant speed, past one or more linear sensor arrays.
Background
Imaging devices such as fax machines capture images by scanning the image at a known, constant rate. For example, in a typical fax machine, a stepper motor draws the sheet bearing the image through a slot to move the image past a fixed scanning head at a constant rate. At any particular time, the scanning head "sees" only a narrow, linear portion of the image adjacent the scanning head. Because the scan rate is constant and predetermined, the fax machine's control circuity can easily be activated at fixed, sequential time intervals, to transfer the image portion seen during each interval into a buffer. The buffer accumulates the image portions to yield a full digital representation of the scanned image. Instead of moving the image past a fixed scanning head as described above, the image may remain in a fixed position while the stepper motor moves the scanning head past the image at a constant rate, as in a typical flat bed scanner.
Prior art devices like those mentioned above use relatively expensive, bulky stepper motors to maintain the scan rate constant to a high degree of precision. Some prior art devices, such as hand-held scanners, use less bulky encoders coupled to rollers to synchronize the scanning process as the scanner is hand-manoeuvred, at variable speed, over the object being imaged. Although the scan rate varies, it can be determined by electricaland/or mechanical coupling between the roller(s) andencoder(s).
However, such arrangements require expensive high precision encoders and/or considerable mechanical complexity to achieve high resolution in the scanned image.
The present invention provides a method and apparatus for capturing an image of a moving object using one or more linear arrays, without the need for high precision stepper motors, and without the need for mechanically measuring the speed of the object.
Summary of Invention
In one embodiment, the invention provides an imaging apparatus in which a linear sensor array sequentially produces images of segments of an object as the object moves transversely across the array to successively position the segments adjacent the sensor. Sequentially ordered pairs of the segment images are compared to produce an output signal representative of similarity therebetween.
One of the pair of segment images is accumulated in a buffer whenever the comparator output signal is not representative of substantial similarity between the pair of images.
In another embodiment, the invention provides an imaging apparatus in which a first linear sensor array produces, at a first time of occurrence, a first image of a first segment of an object positioned adjacent the first sensor. A second linear sensor array is spaced from the first array by a distance d. At a second time of occurrence, the second array produces a second image of a second segment of the object positioned adjacent the second sensor. A buffer is coupled to the first array. The first image and its time of occurrence are accumulated in the buffer for a successive plurality of the first segments as the object moves across the first array. A comparator is coupled between the buffer and the second array. The comparator compares the second image with each one of a selected plurality of the accumulated first images to determine which one of the accumulated first images is most similar to (i.e. best matches) the second image. An object speed estimator then estimates the object's speed S as an appropriately weighted function ofd/(tj-tD,) [i.e.S d/ (ti- tm)], whereti is the time of occurrence of a selected one of the second images, and t, is the time of occurrence of the first image most similar to the selected second image.
The imaging apparatus may be operated at either a fixed or a variable sampling rate. If the sampling rate is fixed, the segment images are produced during sampling intervals of the same duration. Since the speed and time duration of each of the "best match" scans is known, the width of each such scan is readily determinable and the buffer can be sampled to extract equal width image "strips" therefrom which can be assembled to yield the full image.
If a variable sampling rate is used, each segment image is produced during a sampling interval having a duration equal to1/(R * S) where R is the desired (fixed) resolution of the final image. Because the scan rate changes in direct proportion to the object's speed, the composite image can be read directly from buffer as soon as the scanning process is complete.
Further embodiments of the invention incorporate additional sensor arrays to more accurately and robustly measure the object's speed and consequently improve the resolution of the final image.
Brief Description of Drawinqs
Figure 1 is a schematic, oblique perspective illustration of an imaging apparatus having a single linear sensor array.
Figure 2 is a side elevation view of the Figure 1 apparatus.
Figure 3 is a schematic block diagram representation of the electronic components of the Figure 1 apparatus.
Figure 4 is a flowchart illustrating the sequence of steps by which the Figure 1 apparatus forms an image of a moving object.
Figure 5 is a top plan view of a pair of spaced linear sensor arrays.
Figure 6 is a side elevation view of an imaging apparatus incorporating the Figure 5 linear sensor arrays.
Figure 7 is a stylized representation depicting accumulation in a storage buffer of a composite image formed of selected image segments obtained via the Figure 5 linear sensor arrays.
Figure 8 is a flowchart illustrating the sequence of steps by which the Figure 6 apparatus forms an image of a moving object.
Figure 9 is a flowchart illustrating an alternative sequence of steps by which the Figure 6 apparatus forms an image of a moving object.
Figure 10 is a top plan view of three spaced linear sensor arrays.
Figure 11 is a flowchart illustrating the sequence of steps by which imaging apparatus incorporating the Figure 10 linear sensor arrays forms an image of a moving object.
Figure 12 is a top plan view of four spaced, colour filtered linear sensor arrays.
Figure 13 is a side elevation view of an imaging apparatus incorporating the Figure 12 linear sensor arrays.
Figure 14 is a flowchart illustrating the sequence of steps by which the Figure 13 apparatus forms a colour image of a moving object.
Description
Figures 1 and 2 depict a first embodiment of the invention incorporating a single linear sensor array 10.
The object 12 which is to be imaged moves, at an unknown variable or constant speed, in the direction of arrow 14 over viewing region 16 in cover plate 18. Sensor 10 "sees" a narrow linear segment of object 12 through viewing region 16 and produces an output signal representative of that segment. Lens 20, or other means, assists in viewing the object segment seen by sensor 10.
Sensor 10 may be a 1 x n pixel linear array. Cover plate 18 may be transparent, in which case viewing region 16 may be a predefined area of cover plate 18. Alternatively, viewing region 16 may be a slit or aperture in cover plate 18.
As schematically depicted in Figure 3, the output signal produced by sensor 10 is transmitted to a processor 22 which stores the output signal in memory buffer 24.
When a complete (or partial) image of object 12 has been accumulated in buffer 24 as described below, processor 22 outputs the complete (or partial) image at 26.
Operation of the apparatus depicted in Figures 1-3 is illustrated by the Figure 4 flowchart. The signal currently being produced by sensor 10 is received by processor 22 as indicated at step 30 (i.e. sensor 10 is scanned to obtain a 1 x n pixel image of the segment of object 12 currently adjacent viewing region 16). The signal currently produced by sensor 10 (which typically consists of a series of n bytes, with each byte corresponding to one pixel in sensor 10) is compared by processor 22 with the previously scanned signal stored in buffer 24, as indicated at step 32. If comparison step 32 reveals, at step 34, that the signal currently produced by sensor 10 is substantially similar to the previously scanned signal stored in buffer 24, then the aforementioned steps are repeated, commencing with step 30. Otherwise, if comparison step 32 reveals substantial dissimilarity between the signal currently produced by sensor 10 and the previously scanned signal, then the signal currently produced by sensor 10 is stored in buffer 24 as indicated at step 36. If storage step 36 does not fill buffer 24 (i.e. the result of test step 38 is negative) then the aforementioned steps are repeated, commencing with step 30. Otherwise, if storage step 36 fills buffer 24 operation terminates at step 40, leaving the full image in buffer 24.
Those skilled in the art will appreciate that buffer 24 is initially cleared prior to commencement of the image scanning operation. This corresponds to storage, in buffer 24, of a series of blank "previously scanned" image sig nals. It will also be understood that determination, by step 34, of "substantial similarity" between the current and previously scanned signals depends upon the test used to compare the signals, which may be varied to suit the nature of the data comprising such signals. Further, it is not essential to compare the signal currently produced by sensor 10 with the immediately previously scanned signal; previously scanned signals could be stored in a buffer and the comparison made with a selected one of the stored signals.
Persons skilled in the art will also recognize that a variety of techniques can be used to indicate commencement of the image scanning process; or, to indicate termination of the process. For example, an externally provided trigger signal, or initial detection of an output signal from sensor 10, or repetitive checking of sensor 10 for an output signal different from a predefined "scanning nonstarted" signal, are different conditions which could be detected to indicate commencement of the scanning process with step 30. To indicate termination of the process (i.e.
to perform test step 38) one could check to see if the last performance of step 36 had filled buffer 24 to capacity, or determine that a predefined time interval had elapsed with no detection of "substantially dissimilar" data during step 34, or provide an external trigger signal to indicate complete passage of object 12 beyond viewing region 16, etc.
Figure 5 depicts an alternative sensor having first and second parallel linear arrays 42, 44 which are spaced apart by a distance "d". Arrays 42, 44 may each be 1 x n pixel linear arrays. The Figure 6 imaging apparatus incorporating arrays 42, 44 is similar to that described above except that two spaced, parallel viewing regions 46, 48 are provided in cover plate 18. Array 44 "sees" a different segment of object 12 than the segment seen by array 42.
More particularly, since array 44 is spaced a distance "d" behind array 42, array 42 sees a segment of object 12 which is spaced a distance "d" ahead of the segment seen by array 44. As shown in Figure 7, array 42 is used to derive the segments which are stored in buffer 24, while array 44 is used to determine which of the previously scanned segments stored in buffer 24 is most similar to the object segment currently seen by array 44.
For purposes of simplification, Figure 6 shows viewing regions 46, 48 spaced apart by the same distance "d" as arrays 42, 44. However, it is not essential for the viewing regions and arrays to have the same separation distance. The relationship between the viewing regions and arrays is determined by lens 20, or other means. Well known techniques can easily be applied to determine the location and size of the viewing region "seen" by each array. This applies to any embodiment of the invention employing two or more spaced sensor arrays.
The Figure 8 flowchart depicts a method of operating the imaging apparatus depicted in Figures 6-7, using a fixed sampling rate. The signals produced by each of sensors 42, 44 at fixed time sampling intervals having times of occurrencetl, t2, ...tn are received as indicated at step 50 (i.e. sensors 42, 44 are scanned to obtain two 1 x n pixel images of the two segments of object 12 which are respectively currently adjacent viewing regions 46, 48). For each time interval, the scanned image signal produced by array 42 is stored in buffer 24, together with a signal representative of that signal's time of occurrence, as indicated at step 52. At step 54, a selected plurality of the previously scanned signals stored in buffer 24 are compared with the scanned image signal produced by array 44 to find the stored signal which best matches (i.e. which is most similar to) the scanned image signal produced by array 44. The speed S of object 12 is then determined, at step 56, as d/(tj -t",), where tj is the time of occurrence of a selected one of the scanned image signals produced by array 44, andt, is the time of occurrence of the stored signal which best matches the selected array 44 signal. (Note that tj = tj if sensor arrays 42, 44 are scanned simulta neously.) At step 58, the speed information is stored in buffer 24 by appending the speed information to or otherwise associating it with the stored signal which best matches the scanned image signal produced by array 44. As indicated by test step 60, the aforementioned steps are repeated, commencing with step 50, until the scanning process is finished. Because arrays 42, 44 are spaced as aforesaid, steps 50, 52 are typically repeated a plurality of times for different segments as object 12 moves over viewing region 46 before reaching viewing region 48.
Once the scanning process is finished, the composite image is formed, at steps 62-64, by sequentially extracting image "strips" of equal width from the scanned image signals stored in buffer 24. Since the speed S and time duration of each of the "best match" scans is known, the widthwi of each such scan is easily determined aswi =S*t and accordingly buffer 24 can easily be sampled to extract equal width image strips therefrom.
The Figure 9 flowchart depicts an alternative method of operating the Figure 6-7 imaging apparatus, using realtime scan rate control. Steps 70, 72, 74 and 76 are identical to Figure 8 steps 50, 52, 54 and 56 respectively, except that whereas the Figure 8 method used a fixed sampling rate, the Figure 9 method uses a variable sampling rate which is determined by the (variable) speed S of object 12 and the desired (fixed) resolution R of the final image.
Thus, in the Figure 9 method, each sampling intervaltl, t2,... tn has a variable duration Twait = 1/(R * S) which is determined at step 78, after determination of the current speed S of object 12 at step 76. Because the Figure 9 method normalizes the scan rate as a function of speed, the composite image can be read directly from buffer 24 at step 82 as soon as the scanning process is complete, whereas the
Figure 8 method requires normalization of the width of each image strip, as previously explained. It can thus be seen that the Figure 9 method produces the final image more quickly than the Figure 8 method. However, the Figure 9 method is more complex than the Figure 8 method. For example, a faster, more expensive version of processor 22 may be required to reliably implement the Figure 9 method.
By increasing the number of sensor arrays one may more accurately and robustly measure the speed of object 12 and consequently improve the reconstruction of the final image.
For example, Figure 10 depicts a sensor having first, second and third parallel linear arrays 84, 86, 88. First and second arrays 84, 86 are spaced apart by a distance d12; second and third arrays 86, 88 are spaced apart by a distance d23; and, first and third arrays 84, 88 are spaced apart by a distancedl3 =dl2 + d23. Arrays 84, 86 and 88 may each be 1 x n pixel linear arrays, and they may be employed in an imaging apparatus like that depicted in Figure 6 except that a third viewing region is required in cover plate 18 for the third sensor array. Arrays 84, 86 and 88 each "see" different segments of object 12. More particularly, array 86 sees a segment of object 12 which is spaced a distancedl2 ahead of the segment seen by array 84; and, array 88 sees a segment of object 12 which is spaced a distance d23 ahead of the segment seen by array 86 and which is also spaced a distancedl3 ahead of the segment seen by array 84.
The Figure 11 flowchart depicts a method of operating an imaging apparatus incorporating the Figure 10 triple linear array sensor, using a fixed sampling rate. The
Figure 11 method is identical to the Figure 8 method, except that whereas the Figure 8 method is adapted to operation of the Figure 5 dual linear array sensor, the
Figure 11 method is adapted to operation of the Figure 10 triple linear array sensor. Thus, at step 90, the signals produced by each of sensors 84, 86, 88 at fixed time sampling intervals having times of occurrenceti, t2, ...tn are received as three 1 x n pixel images of the three segments of object 12 seen by the three sensors at the respective sample times. For each time interval, the scanned image signal produced by the first array 84 is stored in buffer 24, together with a signal representative of that signal's time of occurrence, as indicated at step 92. At step 94, the previously scanned signals stored in buffer 24 are compared with the scanned image signals produced by both second array 86 and third array 88 to find the stored signal most similar to (i.e. which best matches) the scanned image signal produced by first array 84. The speed
S of object 12 is then determined, at step 96, as an appropriately weighted function ofdl2/ (tj -try), d23/ (t,ll -to), anddl3/ (tk -to) [i.e. S ocdo2/ (tj -tom) , d23/ (trn - to), andwhere (tk -to) ]; where tj is the time of occurrence of a selected one of the scanned image signals produced by array 86, tk is the time of occurrence of a selected one of the scanned image signals produced by array 88,t,,l is the time of occurrence of the previously stored array 84 signal which best matches the selected array 86 image signal, and to is the time of occurrence of the previously stored array 84 signal which best matches the selected array 88 signal.
At step 98, the speed information is stored in buffer 24 by appending the speed information to or otherwise associating it with the stored signal which best matches the scanned image signal produced by array 84. As indicated by test step 100, the aforementioned steps are repeated, commencing with step 90, until the scanning process is finished. Once the scanning process is finished, the composite image is formed, at steps 102-104, by sequentially extracting image "strips" of equal width from the scanned image signals stored in buffer 24, as discussed above in relation to step 62 of Figure 8.
The invention also facilitates capture of colour images. For example, Figure 12 depicts a sensor having four parallel linear arrays 106, 108, 110 and 112. Array 106 is covered by a red band-pass filter and accordingly "sees" only the red portion of the colour spectrum.
Similarly, arrays 108, 110 are covered by green and blue band-pass filters respectively and thus "see" only green and blue portions of the colour spectrum respectively.
Array 112 has no filter (or may have a transparent cover) and accordingly "sees" the full colour spectrum. Arrays 106, 108 are spaced apart by a distance "d". Arrays 108, 110 and 110, 112 may be similarly spaced, although as noted above it is not essential that the array spacing be equal in any embodiment of the invention.
The Figure 13 imaging apparatus incorporating arrays 106, 108, 110, 112 is similar to that described above in relation to Figure 6 except that four spaced, parallel viewing regions 114, 116, 118, 119 are provided in cover plate 18. For ease of reference, sensor arrays 106, 108, 110, 112 are hereafter respectively designated "R" (red),"G" (green), "B" (blue) and "C" (clear), as indicated in
Figures 12-14.
The Figure 14 flowchart depicts a method of operating the Figure 13 colour imaging apparatus, using a fixed sampling rate. The Figure 14 method is identical to the
Figure 8 and 11 methods, except that whereas the Figure 8 and 11 methods are respectively adapted to the operation of dual and triple linear array sensors, the Figure 14 method is adapted to operation of the Figure 12 quadruple linear array colour sensor. Thus, at step 120, the signals produced by each of the R, G, B and C sensors at fixed timesampling intervals having times of occurrence t1 , t2, ... tn are received as four 1 x n pixel images of the four segments of object 12 seen by the four sensors at the respective sample times. For each time interval, the scanned
R image signal produced by the R sensor is stored in an buffer, the scanned G image signal produced by the G sensor is stored in a "G" buffer, and the scanned B image signal produced by the B sensor is stored in a "B" buffer. In each such case, a signal representative of the stored R, G or B image signal's time of occurrence is also stored in the respective R, G and B buffers, as indicated at step 122. At step 124, the previously scanned signals stored in the R, G and B buffers are compared with the scanned image signal produced by the C sensor to find the stored R signal most similar to (i.e. which best matches) the scanned C image signal, the stored G signal which best matches the scanned C image signal, and the stored B signal which best matches the scanned C image signal. Assuming the sensor arrays to be equally spaced, the speed S of object 12 is then determined, at step 126, as an appropriately weighted function of3d/(t1 -tk), 2data - t,) andd/(t1 -tB), wheret1 is the time of occurrence of a selected one of the C image signals, andtR, tG and tB are respectively the times of occurrence of the stored R, G and B signals which best match the selected C image signal. At step 128, the speed information is stored in the R, G and B buffers respectively, by appending the speed information to or otherwise associating it with the stored R, G and B signals which best match the scanned C image signal. As indicated by test step 130, the aforementioned steps are repeated, commencing with step 120, until the scanning process is finished. Once the scanning process is finished, the R, G and
B components of the image are formed, at steps 132-134, by sequentially extracting image "strips" of equal width from the scanned image signals stored in the R, G and B buffers respectively. The R, G and B image components are then merged in well known fashion to yield the final, composite image.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof.
For example, although operation of the Figure 10 and 12 sensors has been described with reference to a fixed sampling rate, those skilled in the art will appreciate that either sensor could alternatively be operated using realtime scan rate control, as described above with reference to Figure 9 for the dual array sensor of Figure 5. Those skilled in the art will also appreciate that non-optical sensors such as capacitive linear arrays may be used as the linear sensor arrays referred to herein.
As another example, although the colour imaging apparatus of Figures 12-13 has been described as having four sensors, those skilled in the art will understand that the "C" sensor may be eliminated if it can be assumed that the object being imaged is sufficiently multi-spectral in colour to facilitate adequate correlation between the R, G and B sensors without a base reference.
As another example, non-optical linear array sensors such as capacitive sensors, electric field sensors, thermal sensors, or other sensor types may be employed. Those skilled in the art will accordingly understand that any one of sensor array 10 (Figures 1 and 2), sensor arrays 42, 44 (Figures 5, 6 and 7) or sensor arrays 84, 86, 88 (Figure 10) could be a non-optical sensor array.
As a further example, one may substitute for any of the aforementioned 1 x n pixel linear arrays anm x n pixel"area" array, wherem 2 2 (i.e.m rows, each having n pixels). Thus, instead of using three discrete 1 x n pixel linear arrays as shown in Figure 10, one could use, say, two or more discrete area arrays of 10 x n pixels. As another alternative, one could employ a single area array of say, 500 x n pixels, scan that array two or more times, and inspect rows having spacings corresponding to the spacings depicted in Figure 10. Persons skilled in the art will readily appreciate that any desired combination of rows of such an area array could be scanned as hereinbefore described in the context of discrete linear arrays. The scope of the invention is to be construed in accordance with the substance defined by the following claims.
